We propose to comprehensively analyze the genetic polymorphisms of class II genes in a collection of mouse strains which are homozygous for H-2 haplotypes derived from 5 separate sub-species of Mus. The class II genes and gene-products of these wild mouse-derived H-2 haplotypes will be compared and they will be gouped into allelic families on the basis of structural similarities. The functional, structural, and genetic properties of these families of class II gene alleles will then be studied in detail. The purpose of this study is to assess the evolutionary mechanisms responsible for the production and maintenance of class II gene polymorphisms. The genetic mechanisms which generate class II gene diversity will be studied by comparing the DNA sequences of structural gene exons which have recently diverged. This analysis will determine whether copy mechanisms or gene conversion is involved in the generation of class II gene diversity. The presence of mutational "hot spots" in the I region will be tested by the analysis of I region restriction site polymorphisms with class II gene DNA probes. Finally, the evolutionary stability of specific class II alleles and class II gene haplotypes will be assessed by comparisons of class II gene alleles prevalent in separate sub-species of Mus. The analysis of class II gene polymorphism in wild mice is a useful model system for the analysis of class II genes in human populations. Our studies of wild mice suggest that a limited number of distally-related allelic families of class II genes may predominate in natural populations. Class II alleles in the same family encode A molecules with very similar antigenic phenotypes and structural properties. However, our functional analysis of these closely-related alleles indicate that the minor structural variations which distinguish their products are often capable of stimulating strong mixed lymphocyte reactions and acute skin graft rejections. These observations in wild mice may be relevant to the poor success rate of allograft survival between DR-identical, genetically unrelated donor-recipient pairs in human transplantation studies. We are in the process of searching for minor structural variations in the class II molecules of DR-identical individuals.